1. Field of the Invention
The present invention relates to a voltage controlled oscillator capable of changing an oscillation frequency by voltage control and a phase-locked oscillator using the same.
2. Description of the Background Art
Conventionally, phase-locked oscillators (PLOs) using voltage controlled oscillators have been used as microwave oscillators for oscillating at microwave frequencies.
FIG. 17 is a block diagram showing an example of the configuration of a conventional frequency division type phase-locked oscillator.
In FIG. 17, the phase-locked oscillator comprises a reference signal source 2, a phase comparator 3, a low-pass filter 4, a voltage controlled oscillator (hereinafter referred to as VCO) 10, a power distributor 9, and a frequency divider 5.
The reference signal source 2 generates a reference signal. The phase comparator 3 compares the phase of the reference signal generated by the reference signal source 2 with the phase of a frequency division signal fed from the frequency divider 5, described later, and outputs a phase difference signal corresponding to a phase difference between the signals. The low-pass filter 4 passes a low frequency component of the phase difference signal outputted from the phase comparator 3, and feeds the low frequency component to a control terminal 111 of the VCO 10 as a control voltage Vc.
The VCO 10 outputs to an output terminal 112 an output signal Out having a frequency corresponding to the control voltage Vc at the control terminal 111. The output signal Out at the output terminal 112 of the VCO 10 is outputted to an output terminal 16 by the power distributor 9, and is fed to the frequency divider 5 as a feedback signal. The frequency divider 5 frequency-divides the feedback signal fed from the power distributor 9, and feeds the feedback signal to the phase comparator 3 as a frequency division signal. In such a way, a phase-locked loop is configured.
FIG. 18 is a block diagram showing an example of the configuration of a conventional sampling type phase-locked oscillator.
In FIG. 18, the phase-locked oscillator comprises a reference signal source 2, a sampling phase detector (hereinafter referred to as SPD) 6, a low-pass filter 4, a VCO 10, and a power distributor 9.
The reference signal source 2 generates a reference signal. The SPD converts the reference signal generated by the reference signal source 2 into a pulse train, samples a feedback signal fed from the power distributor 9, described later, using the pulse train, to detect a relative phase difference between the reference signal and the feedback signal, and feeds a phase difference signal to the low-pass filter 4. The low-pass filter 4 passes a low frequency component of the phase difference signal fed from the SPD 6, and feeds the low frequency component to a control terminal 111 of the VCO 10 as a control voltage Vc.
The VCO 10 outputs to an output terminal 112 an output signal Out having a frequency corresponding to the control voltage Vc at the control terminal 111. The output signal Out at the output terminal 112 of the VCO 10 is outputted to an output terminal 16 by the power distributor 9, and is fed to the SPD 6 as a feedback signal. In such a way, a phase-locked loop is configured.
In each of the phase-locked oscillators shown in FIGS. 17 and 18, when a load connected to the output terminal 16 varies, an oscillation frequency is changed. Therefore, JP-A-60-53306, for example, has proposed that in order to stabilize the oscillation frequency against the variation in the load, an output circuit composed of an attenuator, a buffer amplifier, an isolator, or the like is added to an oscillation circuit in the VCO, to separate the VCO and the load.
FIG. 19 is a block diagram showing the configuration of the VCO 10 in each of the phase-locked oscillators shown in FIGS. 17 and 18.
The VCO 10 comprises an oscillation circuit 100 and an output circuit 110. The output circuit 110 is composed of an attenuator, a buffer amplifier, an isolator, or the like. A control voltage Vc is fed to the control terminal 111 of the oscillation circuit 100. A power supply voltage Vdd is fed to a power supply terminal 114 of the oscillation circuit 100 by a DC power supply. Further, the oscillation circuit 100 is connected to the output terminal 112 through the output terminal 110 composed of an attenuator or the like.
In the conventional VCO 10, the output circuit 110 is thus inserted between the oscillation circuit 100 and the output terminal 112, thereby making it possible to stabilize the oscillation frequency against the variation in the load.
In the above-mentioned conventional phase-locked oscillator, the output circuit 110 is inserted between the oscillation circuit 100 in the VCO 10 and the output terminal 112. Accordingly, the output power of the oscillation circuit 100 is attenuated by passing through the output circuit 110. Consequently, the power of the feedback signal returned to the frequency divider 5 or the SPD 6 is attenuated. In order to obtain a feedback signal having predetermined power, therefore, the output power of the oscillation circuit 100 must be increased in consideration of the amount of attenuation by the output circuit 110. As a result, power consumption is increased.
An object of the present invention is to provide a voltage controlled oscillator capable of reducing the output power of an oscillation circuit while stabilizing an oscillation frequency against the variation in a load and a phase-locked oscillator using the same.
A voltage controlled oscillator according to an aspect of the present invention comprises a control terminal receiving a control voltage; an output terminal; a feedback terminal; an oscillation circuit that generates a signal having a frequency corresponding to the control voltage at the control terminal; a power supply terminal for applying a power supply voltage to the oscillation circuit; an output circuit that outputs to the output terminal the signal generated by the oscillation circuit; and a distribution circuit that distributes a part of the signal generated by the oscillation circuit to the feedback terminal as a feedback signal.
In the voltage controlled oscillator according to the present invention, the signal having the frequency corresponding to the control voltage at the control terminal is generated by the oscillation circuit, and is outputted to the output terminal by the output circuit. In this case, the output circuit is inserted between the oscillation circuit and the output terminal. Therefore, the oscillation frequency of the oscillation circuit is prevented from being changed by the variation in a load connected to the output terminal.
Furthermore, a part of the signal generated by the oscillation circuit is distributed to the feedback terminal as the feedback signal, whereby the feedback signal is not attenuated by the output circuit. Consequently, it is possible to reduce the output power of the oscillation circuit which is required to obtain the feedback signal having predetermined power.
Consequently, it is possible to reduce the output power of the oscillation circuit while stabilizing the oscillation frequency against the variation in the load.
In the voltage controlled oscillator, the distribution circuit may comprise a branch circuit that leads to the feedback terminal a signal leaking out to the power supply terminal from the oscillation circuit.
In this case, the signal leaking out to the power supply terminal from the oscillation circuit is used as the feedback signal. Consequently, the feedback signal is not attenuated by the output terminal.
The branch circuit may comprise a capacitor and an amplifier which are connected in series between the power supply terminal and the feedback terminal.
In this case, the passage of a DC component is rejected by the capacitor, and the signal leaking out to the power supply terminal from the oscillation circuit is amplified by the amplifier, and is fed to the feedback terminal as the feedback signal. Consequently, it is possible to further reduce the output power of the oscillation circuit which is required to obtain the feedback signal having predetermined power.
The distribution circuit may comprise a branch circuit that leads to the feedback terminal a signal leaking out to the control terminal from the oscillation circuit.
In this case, the signal leaking out to the control terminal from the oscillation circuit is used as the feedback signal. Consequently, the feedback signal is not attenuated by the output circuit.
The branch circuit may comprise a capacitor and an amplifier which are connected in series between the control terminal and the feedback terminal.
In this case, the passage of a DC component is rejected by the capacitor, and the signal leaking out to the control terminal from the oscillation circuit is amplified by the amplifier, and is fed to the feedback terminal as the feedback signal. Consequently, it is possible to further reduce the output power of the oscillation circuit which is required to obtain the feedback signal having predetermined power.
The distribution circuit may comprise a power distributor that distributes the signal generated by the oscillation circuit between the output circuit and the feedback terminal.
In this case, a part of the signal generated by the oscillation circuit is distributed to the feedback terminal by the power distributor in a stage preceding the output circuit, and is used as the feedback signal. Consequently, the feedback signal is not attenuated by the output circuit.
The voltage controlled oscillator may further comprise an amplifier that amplifies the signal fed to the feedback circuit from the power distributor.
In this case, the signal distributed by the power distributor is amplified by the amplifier, and is fed to the feedback terminal as the feedback signal. Consequently, it is possible to further reduce the output power of the oscillation circuit which is required to obtain the feedback signal having predetermined power.
The output circuit may comprise an attenuator, a buffer amplifier, or an isolator.
In this case, the change in the oscillation frequency of the oscillation circuit by the variation in the load connected to the output terminal is prevented by the attenuator, the buffer amplifier, or the isolator.
A phase-locked oscillator according to another aspect of the present invention comprises a reference signal source that generates a reference signal; a voltage controlled oscillator that outputs a signal having a frequency corresponding to a control voltage as an output signal and a feedback signal; a phase comparison circuit that compares the phase of the feedback signal from the voltage controlled oscillator or a signal based on the feedback signal with the phase of the reference signal generated by the reference signal source to output a phase difference signal representing a phase difference between the signals; and a control voltage application circuit that applies the phase difference signal outputted from the phase comparison circuit to the voltage controlled oscillator as the control voltage, the voltage controlled oscillator comprising a control terminal receiving the control voltage, an output terminal, a feedback terminal, an oscillation circuit that generates a signal having a frequency corresponding to the control voltage at the control terminal, a power supply terminal for applying a power supply voltage to the oscillation circuit, an output circuit that outputs to the output terminal the signal generated by the oscillation circuit, and a distribution circuit that distributes a part of the signal generated by the oscillation circuit to the feedback terminal as the feedback signal.
In the phase-locked oscillator according to the present invention, the reference signal is generated by the reference signal source. Further, the signal having the frequency corresponding to the control voltage is outputted as the output signal and the feedback signal by the voltage controlled oscillator. The phase of the feedback signal from the voltage controlled oscillator or the signal based on the feedback signal and the phase of the reference signal generated by the reference signal source are compared with each other by the phase comparison circuit, so that the phase difference signal representing the phase difference is outputted, and is applied to the voltage controlled oscillator as the control voltage by the control voltage application circuit. Therefore, a phase-locked loop is configured.
In the voltage controlled oscillator, the signal having the frequency corresponding to the control voltage at the control terminal is generated by the oscillation circuit, and is outputted to the output terminal by the output circuit. In this case, the output circuit is inserted between the oscillation circuit and the output terminal. Therefore, the oscillation frequency of the oscillation circuit is prevented from being changed by the variation in a load connected to the output terminal.
Furthermore, a part of the signal generated by the oscillation circuit is distributed to the feedback terminal as the feedback signal, whereby the feedback signal is not attenuated by the output circuit. Consequently, it is possible to reduce the output power of the oscillation circuit which is required to obtain the feedback signal having predetermined power.
Consequently, it is possible to reduce the output power of the oscillation circuit while stabilizing the oscillation frequency against the variation in the load.
The phase-locked oscillator may further comprise a frequency divider that frequency-divides the feedback signal outputted form the feedback terminal of the voltage controlled oscillator to output a frequency division signal, and the phase comparison circuit may comprise a phase comparator that compares the phase of the frequency division signal outputted by the frequency divider with the phase of the reference signal generated by the reference signal source.
In this case, a frequency division type phase-locked oscillator capable of reducing the output power of an oscillation circuit while stabilizing an oscillation frequency against the variation in a load is configured.
The phase comparison circuit may comprise a sampling phase comparator that converts the reference signal generated by the reference signal source into a pulse train, and samples the feedback signal outputted from the feedback terminal of the voltage controlled oscillator using the pulse train.
In this case, a sampling type phase-locked oscillator capable of reducing the output power of an oscillation circuit while stabilizing an oscillation frequency against the variation in a load is configured.
In the voltage controlled oscillator, the distribution circuit may comprise a branch circuit that leads to the feedback terminal a signal leaking out to the power supply terminal from the oscillation circuit.
In this case, the signal leaking out to the power supply terminal from the oscillation circuit is used as the feedback signal. Consequently, the feedback signal is not attenuated by the output circuit.
The branch circuit may comprise a capacitor and an amplifier which are connected in series between the power supply terminal and the feedback terminal.
In this case, the passage of a DC component is rejected by the capacitor, and the signal leaking out to the power supply terminal from the oscillation circuit is amplified by the amplifier, and is fed to the feedback terminal as the feedback signal. Consequently, it is possible to further reduce the output power of the oscillation circuit which is required to obtain the feedback signal having predetermined power.
The distribution circuit may comprise a branch circuit that leads to the feedback terminal a signal leaking out to the control terminal from the oscillation circuit.
In this case, the signal leaking out to the control terminal from the oscillation circuit is used as the feedback signal. Consequently, the feedback signal is not attenuated by the output circuit.
The branch circuit may comprise a capacitor and an amplifier which are connected in series between the control terminal and the feedback terminal.
In this case, the passage of a DC component is rejected by the capacitor, and the signal leaking out to the control terminal from the oscillation circuit is amplified by the amplifier, and is fed to the feedback terminal as the feedback signal. Consequently, it is possible to further reduce the output power of the oscillation circuit which is required to obtain the feedback signal having predetermined power.
The distribution circuit may comprise a power distributor that distributes the signal generated by the oscillation circuit between the output circuit and the feedback terminal.
In this case, a part of the signal generated by the oscillation circuit is distributed to the feedback terminal by the power distributor in a stage preceding the output circuit, and is used as the feedback signal. Consequently, the feedback signal is not attenuated by the output circuit.
The voltage controlled oscillator may further comprise an amplifier that amplifies the signal fed to the feedback circuit from the power distributor.
In this case, the signal distributed by the power distributor is amplified by the amplifier, and is fed to the feedback terminal as the feedback signal. Consequently, it is possible to further reduce the output power of the oscillation circuit which is required to obtain the feedback signal having predetermined power.
The output circuit may comprise an attenuator, a buffer, or an isolator.
In this case, the change in the oscillation frequency of the oscillation circuit by the variation in the load connected to the output terminal is prevented by the attenuator, the buffer amplifier, or the isolator.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.